Did GM just pop the Facebook bubble? Though the announcement that the auto giant will pull its paid advertising from Facebook is unlikely to seriously undermine the latter’s upcoming IPO, it surely will cast a shadow over the much-hyped event.

The company’s short lifespan and quixotic management have already generated plenty of skepticism about the pricing of the shares, which value the company at more than $100 billion -- or roughly the size of Morocco.

Now its basic business model is under attack.

GM’s news raises two glaring issues confronting would-be investors.

First, the auto maker reports that its $10 million of paid Facebook ads haven’t generated sales.

Second, the company says it will continue to have a presence on Facebook -- by hosting pages which are free.

That its advertising has been ineffective is alarming; that the country’s third-largest advertiser (or anyone else) can copper its bets free of charge highlights the great continuing unknown about the Internet – can companies reliably make money from all the brilliant innovations that have become so central to our lives?

Here’s a secret from someone who used to do this for a living: no one can possibly know what this company is worth. The entire social media space is evolving, advertising is in the midst of a gigantic upheaval, new companies are born every day that are targeting the Facebook audience and the fidelity of the company’s users is a complete unknown. Throw in a couple of economic variables such as the outlook for the recovery and for corporate profits and you have the kind of uncertainty soup that often spills into IPO valuations.

In short, Facebook may well turn out to be a terrific investment, but I wouldn’t bet the ranch.

A heads-up in this department presented itself recently when I was reading through some magazines published in the early days of the financial crisis.

In October 2007, Forbes reviewed stock picks from money manager John Maloney. His best idea? AIG, then selling at $68 per share. The “value-oriented” one-time banker thought the stock was cheap at 11 times earnings, though he worried about a possible “worst nightmare scenario for AIG – meltdowns in its real estate investments and lending.” That risk he deemed tolerable, since it “would shave just 13 cents off its expected 2007 earnings of $7 per share.”

OK, hindsight is 50-50 and I don’t mean to pick on Mr. Maloney. In 2007, few saw the extent of the financial calamity about to change the world, and financial writing from that time teems with disastrous projections. Not only, of course, about finance.

In that same issue of Forbes, there is also a piece about Richard Rosenblatt, who had recently sold MySpace to News Corp. for $580 million. That purchase – thought brilliant at the time -- turned out to be a dud, thanks to the ascent of rival Facebook. After ad sales plummeted, News Corp dumped MySpace last year for roughly $35 million.

In 2007, Rosenblatt was in the midst of putting together a new company – DemandMedia – which went public in January, 2011 at $17 and which is now selling at $8.

The trail of Internet tears is strewn with meteoric successes and dismal failures; the only thing that seems to change is the price tag.

In Facebook’s case, investors are paying for the astounding 500 million+ people who log onto the site every day, and for the extraordinary global reach (80% of its users are outside the U.S. and Canada.) They are not paying for the $3.7 billion in revenues the company reported for last year.

A CNBC/AP poll just out shows that half the country considers Facebook a passing fad, and that the offering price is too high. People under 35 are more optimistic: 59% think the stock offering is a good bet. Alarmingly, though, more than half think the site’s appeal will fade.

Those conflicting views highlight the real impact of the Facebook offering. Forget what the deal means to investors. Think about what it means to our graduates just entering the work force.

Young people today want to be Mark Zuckerberg. They want the overnight riches and success of Instagram – a company established only two years ago and sold to Facebook for a cool billion dollars. Students in our most prestigious business schools are flocking to tech start-ups, often willing to work for no pay – just to have a shot at participating in the next insta-win.

Is this a good thing? Yes and no.

Kids today hate the idea of climbing the corporate ladder; they don’t like hierarchy and cannot imagine “working their way to the top.” They want to start at the top. That impatience will feed the entrepreneurship that has kept the U.S. at the forefront of technology and innovation – so vital to our country’s growth. It’s that energy that brought us Google and Microsoft, and that brings us Facebook.

That’s a great thing.

Should we be concerned that we have spawned a generation of risk-takers? Does it matter that there will be inevitable disappointments?

I haven’t a clue. Those are unknowns – just like the outlook for Facebook’s IPO.